This study involves the investigation of spherically shaped filler diameter and interphase effects on the Young's modulus
of micro and nano size silicon dioxide (SiO2) particle reinforced epoxy composite materials. Specifically, 10μm and
80nm size SiO2 particles and Epon 862 epoxy are chosen as fillers and a matrix material, respectively. While 10μm and
80nm SiO2 particles are dispersed in the epoxy through a direct shear mixing method, nano-composites are fabricated
with hardener at desirable ratios. Both micro- and nano-composites are prepared at 2 different particle loading fractions
for tensile testing. It is observed that the nano-composites show significant increase in Young's modulus over micro-composites,
showing a linear increase as particle volume fraction increases. This could indicate that for nano-composites,
the interphase region between the particle and matrix can considerably affect their mechanical properties. Here, we
develop a finite element analysis (FEA) model to investigate the interphase effect on the Young's modulus of both
micro- and nano-composites. This model demonstrates how to estimate the effective volume fraction of a particle as
filler using a combined experimental/numerical approach. The effective volume fraction is shown to be important in
predicting the mechanical response of nano-scale particles reinforced composite materials.
Recent advances in the production and availability of nanoscale materials has led to a significant interest in the use of
nanoscale fillers in order to augment and tailor material performance in nanostructured composites. A specific area of
interest is the use of high aspect ratio fillers, such as carbon nanotubes (CNT) and carbon nanofibers (CNF) to augment
the damping capacity of nanostructured composites. Previous work has shown the use of high aspect ratio fillers to
significantly enhance the damping capacity at low frequency by more than 100%; however, the enhancement achieved
has been predicated on strain levels in the composite. Our previous studies have indicated a strong strain dependent
response in the nanostructured composites utilizing CNF to augment damping capacity. This is due, in part, to the
random distribution of fiber orientations seen in the nanostructured composites. The random distribution of filler
orientations is thereby relative to the load applied to the composite that results in a critical shear stress thresholds being
surpassed at the nano scale, allowing the filler to slip relative to the matrix, resulting in frictional energy dissipation as
heat and thereby inducing damping to the high aspect ratio filler nanostructured composite. In light of the promise this
technology holds for use in engineered applications requiring specific damping performance, there remains a
fundamental lack in understanding of the precise mechanisms and thereby a lack of ability to accurately predict material
performance, which is limiting application of the technology. This study looks at the effect of the random filler
orientation of CNF included composites and examines the viscoelastic response of the composite specifically
investigating the effect of filler orientation relative to the loading direction and the effect of filler waviness.
Furthermore, this study looks at the strain dependent nature of the viscoelastic response and develops an analytical
modeling tool to look at the effect of the strain dependent viscoelastic response seen in previous studies with the aim of
achieving a better fundamental understanding of the effect of filler orientation and the associated strain dependent nature
of the viscoelastic response seen in high aspect ratio nano- filled composites.
The focus of this study was to experimentally investigate spherically shaped micron-size particles reinforced polymethyl
methacrylate (PMMA) and polycarbonate (PC) polymer composites for improving energy absorbing capabilities such as
toughness and low-velocity impact resistance. In this study, a solution mixing method was developed to fabricate both
PMMA and PC polymer composites with spherically shaped micron-size polyamide- nylon 6 (PA6) particles inclusions.
The morphology of the fracture surfaces of polymer composites was examined by using optical microscopy and
scanning electron microscopy. Strain-rate dependent response of both PMMA and PC polymer composites was
investigated by characterizing tensile and flexural properties. Low-velocity penetration testing was performed for both
polymer composites and the key results observed for energy absorption capabilities are discussed in this study.
Base Epon 862 resin was enhanced with two types of fillers, graphitized carbon nanofiber (CNF) and silicon dioxide
(SiO2) particles. The effect of both filler type and filler loading were investigated with respect to the energy absorbing
capacity as well as the thermal stability of the hybrid composite material, measured in terms of the coefficient of thermal
expansion (CTE). As well the composites with combinations of the fillers were evaluated for both enhanced damping
and thermal stability, making it suitable for structural materials that need multiple functions. The composites were
evaluated with dynamic mechanical analysis (DMA) to evaluate viscoelastic response, and using strain gauges to
measure thermal strain responses. It has been found that the addition of 3wt% SiO2 along with 3wt% CNF can improve
damping loss factors by up to 26% while at the same time improving thermal stability with reductions in CTE of up to
16.5%. Furthermore, these fillers loadings were successfully dispersed as received by mechanical mixing technique,
making fabrication more economically suited to engineering applications.
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